This invention relates to apparatus for building a first stage carcass of a pneumatic tire having a `sealant layer`, interchangeably also referred to as a `sealant strip`, which makes the tire "puncture-proof". Such a tire, referred to as a "sealant tire", is disclosed in U.S. Pat. No. 4,913,209. To build a sealant tire, the sealant layer which is an elastomeric semi-solid, is placed first on a tire building drum, followed by an inner liner, carcass plies, axially spaced annular bead rings, and tread, in the usual manner of constructing a tire. More specifically, the sealant layer and inner liner must be centered upon the building drum, followed by the belt plies of essentially weftless, rubberized fabric which are assembled in the form of a cylindrical body on the drum and then bead rings are anchored into the ends of the plies. Any conventional method may be employed to attach the bead rings to the ply ends; after which the tread is centered upon the body to complete the carcass.
Since the sealant layer is typically from about 0.2 cm to about 2.0 cm thick, and narrower than the width of the inner liner, there was every reason to believe that building a first stage carcass on a conventional expansible flat drum in the conventional manner described hereinbefore, would present no serious problem if the surface of the drum and/or sealant layer was adequately coated with a suitable release coating. Clearly, if the drum was not expansible, the finished carcass would not likely be removable from the drum despite being coated with a release agent, simply because the semi-solid consistency of the sealant layer would not permit removal. No tire building machine with a non-expansible drum could be used, and specifically, the tire building machine disclosed in U.S. Pat. No. 3,489,634 (Class 156/subclass 398) to Pizzo et al cannot be used to build a sealant tire.
However, it was discovered that even a release-coated expansible drum was ill-suited to building a sealant tire carcass. Too often, the sealant layer was unacceptably distorted. In particular, the sealant strip or layer was flattened out and spread over a much wider area than that of the original layer making it impractical to maintain a desired thickness of sealant symmetrically disposed about the circumferential center line of the carcass. It was therefore deemed necessary to provide a wide groove in the surface of the drum, the groove corresponding in width and depth to the width and thickness of the sealant strip.
Since it was evident that the carcass could only be removed from the drum if it was an expansible drum, an expansible drum tire building apparatus was constructed by modifying the construction of the non-expansible drum '634 machine, including providing the drum with a groove which in side elevation presented a profile which mirrored the profile of the sealant strip. Except that, because of the physical properties of the sealant strip, and specifically its viscous semi-solid form, reminiscent of `chewing gum`, which form had to be maintained if the sealant strip was to perform its intended function, it was found that the sealant strip was routinely damaged more often than not, when the built carcass was removed (or attempted to be) from the collapsed drum.
The key to making sealant tire carcasses with an expansible drum having a groove cut in its surface symmetrically about the circumferential center line of the drum, was found to be to provide the groove with contoured opposed sidewalls. The term "contoured" is used to define sidewalls which are tapered, whether smoothly as in an inclined plane, or with interruptions such as steps; or, sidewalls which together define an arc. With such a contoured groove, any expansible drum tire building apparatus, for example those disclosed in U.S. Pat. No. 4,614,562 to Jones (class 156/subclass 420), and more recently U.S. Pat. No. 4,855,008 to Terrado (class 156/subclass 401), inter alia, may be conveniently modified for use in the building of a carcass for sealant tires.